[SCSI] remove a useless get/put_device pair in scsi_next_command

Eliminate a get_device() / put_device() pair from scsi_next_command().
Both are atomic operations hence removing these slightly improves
performance.

[hch: slight changes due to different context]
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

drivers/scsi/scsi_lib.c

@@ -526,14 +526,9 @@ void scsi_next_command(struct scsi_cmnd *cmd)
 	struct scsi_device *sdev = cmd->device;
 	struct request_queue *q = sdev->request_queue;
 
-	/* need to hold a reference on the device before we let go of the cmd */
-	get_device(&sdev->sdev_gendev);
-
 	scsi_put_command(cmd);
-	put_device(&sdev->sdev_gendev);
 	scsi_run_queue(q);
 
-	/* ok to remove device now */
 	put_device(&sdev->sdev_gendev);
 }